Urinalysis highly sensitive and specific for UTI in febrile infants

1. Urinalysis had ≥90% sensitivity and specificity in identifying urinary tract infection (UTI) among infants ≤60 days old with fever, regardless of presence of associated bacteremia.

2. Sensitivity of urinalysis was slightly higher among infants with associated bacteremia compared to those without, however specificity remained constant.

Study Rundown: UTI is a leading cause of major bacterial infection in infants ≤60 days old, however due to variability in test performance and urine collection methods, the test characteristics (sensitivity, specificity, etc) for urinalysis in this population are not well defined. Researchers in this study analyzed data from emergency department visits to determine the sensitivity and specificity of urinalysis in identifying UTI in febrile children ≤60 days old, both in aggregate and when stratified by presence of associated bacteremia. In accordance with variability in current literature, this study used 2 definitions of UTI: growth of either ≥50,000 or ≥10,000 colony-forming units (CFUs) per mL of uropathogen. Results demonstrated ≥90% sensitivity (with UTI defined as ≥50,000 CFUs/mL) for aggregate and stratified data, with slightly higher sensitivity among patients with bacteremia. Test specificity was also ≥90% and remained constant irrespective of colony count threshold or bacteremia status. The study is limited by definition of UTI based on urine culture alone, while the American Academy of Pediatrics definition recommends culture plus presence of pyuria or bacteriuria; therefore, some patients with asymptomatic bacteriuria may have been included in this analysis. Nonetheless, these findings suggest urinalysis is a reliable and accurate way to diagnosis UTI in infants ≤60 days old with fever.

In-depth [cross-sectional]: Investigators performed a secondary analysis of data collected from a previous study conducted at 26 emergency departments across the United States between 2008-2013. Participants included a subset of 4147 previously healthy, full-term infants ≤60 days old presenting with fever ≥38°C to 1 of the relevant emergency departments. Test characteristics for urinalysis (defined as positive if positive leukocyte esterase or nitrite, or pyuria >5 WBCs/HPF) in diagnosing UTI were determined for aggregate data, as well as for patients with and without associated bacteremia. In total, 289 (7.0%) of the study patients had UTIs with growth of ≥50,000 CFUs/mL, 27 (9.3%) of whom had associated bacteremia. 106 additional patients (n=395, 9.5%) had UTI using the later definition. Results showed that the sensitivity and specificity of the aggregate urinalysis were 0.94 (95% CI 0.8\91-0.97) and 0.91 (95% CI 0.90-0.91) respectively. When stratified by presence of bacteremia, sensitivity for patients was higher for patients with bacteremia (1.00, 95% CI 0.87-1.00) compared to those without (0.94, 95% CI 0.90-0.96). The specificity remained the same even after stratification. When analyzing patients diagnosed with UTI defined as ≥10,000 CFUs/mL, urinalysis sensitivity overall was 0.87 (95% CI 0.83-0.90) again with a higher sensitivity among patients with bacteremia compared to those without (1.00, 95% CI 0.88-1.00 and 0.86, 95% CI 0.82-0.89, respectively). Using the latter criteria, test specificity did not change.

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